As the information recording medium on which copyrighted work information such as a piece of music, image, etc. can be recorded in a digital form, there are widely known read-only optical discs such as a CD (compact disc), DVD (digital versatile disc) and the like.
Copyrighted work information can be recorded on an optical disc such as a CD or DVD by forming, on a disc-shaped substrate of the latter, a land/pit pattern corresponding to a digital form of the copyrighted work information. A disc master having such copyrighted work information thus recorded thereon can be replicated to produce and sell a large number of optical discs carrying the same copyrighted work information.
So, in marketing such optical discs, it is necessary to prevent the optical disc from being illegally copied and the copyright on work information recorded on the optical disc from being infringed. However, since read-only optical discs are designed to have only same information recorded thereon, they cannot be differentiated from each other. That is, the read-only optical disc is not necessarily desirable from the standpoint of medium management.
As a solution to the problems in the medium management of the optical discs, there is available a method of additionally recording medium-unique information different from one medium to another on a part of each read-only optical disc. By additionally writing medium-unique information to each medium, it is possible to build a system in which a disc player reads the medium-unique information on an optical disc and which sends it to a server via a network. In case illegal copies of an optical disc having copyrighted work information recorded thereon are produced and marketed without permission of the copyright holder, many pieces of the same medium-unique information will be detectable by such a system via the network, by which it is alarmed that the illegal copies of the optical disc in consideration are on the market. Further, the detected medium-unique information can be traced to ascertain a person having illegally copied the optical disc without permission and also prevent such illegal copying. Recording of such medium-unique information on each read-only optical disc can be a very effective solution to the problem of such an illegal copying of a read-only optical disc.
Even a piece of medium information unique to each title of work information recorded on an optical disc will be useful to protect the copyright on the work information as long as it is recorded in such a manner that it cannot easily be copied by any commercially available recorder/player.
It is well known to utilize the “Postscribed ID (trademark)” developed by the Sony and Sony Disclosure for additionally writing an Identifier unique to each optical medium to a portion of the optical disc where work information as a content or the like is recorded in the form of a land/pit pattern.
The method utilizing the “Postscribed ID” will be explained herebelow. An optical disc such as a CD of which the reflecting layer as a recording layer is formed from a material that can be melted by additional-writing light is produced once. Next, a land in a predetermined portion of a land/pit pattern formed on a recording track of the optical disc is concaved, namely, transited to a pit by irradiating a high-power laser beam.
An area where the land may be transited to a pit is provided in a plurality of predetermined portions on a read-only optical disc, it is decided based on information unique to the optical disc whether each of the land portions is to be transited to a pit or left as it is, and the unique disc information is additionally written in the area where actual work information as a content or the like is recorded.
In case the above Postscribed ID is utilized since it is necessary that a location where the Postscribed ID is recorded should be detectable by a player for the optical disc, the portion of the optical disc where a land is transited to a pit should be limited to a predetermined portion of the optical disc. Further, if a data row that will not comply with a modulation rule after the land is transited to a pit, the optical disc will not be playable. So, it is necessary to abide by the modulation rule also after the land is transited to a pit.
A recording rule having solved the above problems with a CD or DVD adopting the EFM (eight-fourteen modulation) or EFM+ technique is disclosed in the Japanese Patent Application Laid-Open Disclosure No. 2003-141742 and Japanese Patent Gazette No. 2003-151145.
Recently, there has been proposed a BD (blue-ray) disc (will be referred to as “SD disc” hereunder) as a recording medium of a generation next to the CD and DVD. A read-only BD disc should desirably have an Identifier additionally recorded thereon with an Identifier recording technique such as the aforementioned Postscribed ID.